1. Field of Invention
This invention is an implant for placement in the human body and an assembly for so placing that implant. Most desirably, it is an implant for use in the vasculature of the human body and is used to occlude a cavity or space in that vasculature as a portion of a treatment regimen. The implant itself is preferably a component of a deployment device or assembly using an electrolytically severable joint or a selected portion of a wire connected to the implant.
2. Description of the Prior or Related Art
Implants may be placed in the human body for a wide variety of reasons. For instance, stents are placed in a number of different lumens in the body. They may be placed in arteries to cover vascular lesions or to provide patency to the vessel. Stents are also placed in biliary ducts to prevent them from kinking or collapsing. Grafts may be used with stents to promote growth of endothelial tissue within those vessels. Vena cava filters are implanted in the body, typically in the vena cava, to catch thrombus which are sloughed off from other sites within the body and which may be in the blood passing through the chosen site.
Vaso-occlusive devices or implants are used for a wide variety of reasons. They are often used for treatment of intra-vascular aneurysms. This is to say that the treatment involves the placement of a vaso-occlusive device in an aneurysm to cause the formation of a clot and eventually of a collagenous mass containing the vaso-occlusive device. These occlusions seal and fill the aneurysm thereby preventing the weakened wall of the aneurysm from being exposed to the pulsing blood pressure of the open vascular lumen.
Treatment of aneurysms in this fashion is a significant improvement over the surgical method typically involved. The surgical or extravascular approach is a common treatment of intracranial berry aneurysm; it is straightforward but fairly traumatic. The method involves removing of portion of the cranium and locating the aneurysm. The neck of the aneurysm is closed typically by applying a specially sized clip to the neck of the aneurysm. The surgeon may choose to perform a suture ligation of the neck or wrap the entire aneurysm. Each of these procedures is performed by an very intrusive invasion into the body and is performed from the outside of the aneurysm or target site. General anesthesia, craniotomy, brain retraction, and a placement of clip around the neck of the aneurysm all are traumatic. The surgical procedure is often delayed while waiting for the patient to stabilize medically. For this reason, many patients die from the underlying disease prior to the initiation of the surgical procedure.
Another procedurexe2x80x94the extra-intravascular approachxe2x80x94involves surgically exposing or stereotaxically reaching an aneurysm with a probe. The wall of the aneurysm is perforated from the outside and various techniques are used to occlude the interior of the aneurysm to prevent its rebleeding. The techniques used to occlude the aneurysm include electro-thrombosis, adhesive embolization, hoghair embolization, and ferromagnetic thrombosis. These procedures are discussed in U.S. Pat. No. 5,122,136 to Guglielmi et al., the entirety of which is incorporated by reference.
Guglielmi further describes an endovascular procedure which is at once the most elegant and least invasive. The procedure described in that patent includes a step in which the interior of the aneurysm is entered by the use of guidewire such as those in Engelson, U.S. Pat. No. 4,884,579 and a catheter as in Engelson, U.S. Pat. No. 4,739,768. These patents described devices utilizing guidewires and catheters which allow access to aneurysms from remote parts of the body. Typically, these catheters enter the vasculature through the femoral artery in the groin. The Guglielmi system uses catheters and core wires which have a very flexible distal regions and supporting midsections which allow the combinations to be steerable to the region of the aneurysm. That is to say that the guidewire is first steered for a portion of the route to the aneurysm and the catheter is slid up over that guidewire until it reaches a point near the distal end of the guidewire. By steps, the catheter and guidewire are then placed at the mouth of the aneurysm. The catheter is introduced into the aneurysm and vaso-occlusive or embolism forming devices may be delivered through the lumen.
Various vaso-occlusive devices are introduced through the noted microcatheters to close the aneurysm site. In some instances, a small balloon may be introduced into the aneurysm where it is inflated, detached, and left to occlude the aneurysm. Balloons are becoming less in favor because of the difficulty in introducing the balloon into the aneurysm sac, the possibility of aneurysm rupture due to over-inflation of the balloon within the aneurysm, and the inherent risk associated with the traction produced when detaching the balloon.
Another desirable embolism-forming device which may be introduced into aneurysm using end of vascular placement procedure is found in U.S. Pat. No. 4,994,069 to Ritchart et al. In that patent are described various devices, typically platinum/tungsten alloy coils having very small diameters, which may be introduced into the aneurysm through a catheter such as those described in the Engelson patents above. These coils are often made of wire having a diameter of 2-6 mils. The coil diameter is often 10-30 mils. These soft, flexible coils, may be of any length desirable and appropriate for the site to be occluded. After these vaso-occlusive coils are placed in a berry aneurysm, for example, they first cause a formation of an embolic mass. This initial mass or clot is thereafter complemented with a collagenous material which significantly lessens the potential for aneurysm rupture.
There are variety of other vaso-occlusive devices, typically coils which may be delivered to the vascular site in a variety of ways, e.g., by mechanically detaching them from the delivery device. For instance, U.S. Pat. No. 5,234,437, to Sepetka shows a method of unscrewing a helically wound coil from a pusher having interlocking surfaces. U.S. Pat. No. 5,250,071, to Palermo shows an embolic coil assembly using interlocking clasps both on the pusher and on the embolic coil. U.S. Pat. No. 5,261,916, to Engelson shows a combination pusher/vasoocclusive coil assembly joined by an interlocking ball and keyway type coupling. U.S. Pat. No. 5,304,195, to Twyford et al., shows a pusher/vaso-occlusive coil assembly having a fixed proximally extending wire carrying a ball on its proximal end and a pusher having a similar end which two tips are interlocked and disengaged when expelled from the distal tip of the catheter. U.S. Pat. No. 5,312,415, to Palermo shows a method for discharging numerous coils from a single pusher by using a guidewire which has a section capable of interconnecting with the interior of a helically wound coil. U.S. Pat. No. 5,350,397, to Palermo et al. shows a pusher having a throat at its distal end and a pusher through its axis. The pusher throat holds onto the end of an embolic coil and releases that coil upon pushing the axially placed pusher wire against member found on the proximal end of the vaso-occlusive coil. Other mechanically detachable embolism forming devices are known in the art.
Each of the patents listed herein is specifically incorporated by reference.
Guglielmi et al. shows an embolism forming device and procedure for using that device which, instead of a mechanical joint, uses an electrolytically severable joint. Specifically, Guglielmi places a finely wound platinum coil into a vascular cavity such as an aneurysm. The coil is delivered endovascularly using a catheter such as those described above. After placement in the aneurysm, the coil is severed from its insertion core wire by the application of a small electric current to that core wire. The deliverable coils are said to be made of a platinum material. They may be 1-50 cm or longer as is necessary. Proximal of the embolic coil, as noted above, is a core wire which is typically stainless steel. The core wire is used to push the platinum embolic coil into vascular site to be occluded. Other embodiments of the Guglielmi technology is found in U.S. Pat. No. 5,354,295 (hereinafter referenced as the xe2x80x9cGuglielmi systemxe2x80x9d).
This invention is an implant for placement in the human body and an assembly for so placing that implant. In the illustrated embodiment it is an implant for use in the vasculature of the human body and is used to occlude a cavity or space in that vasculature as a portion of a treatment regimen. The implant itself is preferably a component of a deployment device or assembly using an electrolytically severable joint or a selected portion of a wire connected to the implant. The implant is electrically isolated from participating in the electrolysis by electrical insulation between an electrolytically severable joint or portion of the wire by a highly resistive or insulative coupling or by coating of the implant by an a layer of insulation. Such isolation and minimization of the conductive pathway from the placement apparatus to the body""s fluids appears to enhance the susceptibility of the electrolytic joint to quick erosion and detachment of the implant from the deployment media. Although the implant itself is preferably a vaso-occlusive device, it may instead be used for any implantable device which may be installed in this manner.
The improvement involves the use of an insulative or highly resistive member proximal of the implant. The resistive or insulating member may be any suitable material such as inorganic oxides, glues, polymeric inserts, polymeric coverings, etc. This insulative or highly resistive layer or joint appears to focus the current flow through the sacrificial electrolytic joint and thereby improves the rate at which detachment of the implant occurs.
More specifically, the invention is an implant assembly for placement of an implant in the human body in presence of an ionic fluid. An electrolytically severable joint is situated to release the implant member upon application of electrical energy to the electrolytically severable joint. The implant member is electrically isolated from electrolysis in the ionic fluid.
In one embodiment, the electrical isolation from electrolysis is due to an insulative or highly resistive layer interposed between implant member and the electrolytically severable joint. The insulative or highly resistive layer may be comprised of a polymer, such as polyester. The layer may be comprised of any material or combinations of materials now known or later devised which in the aggregate are nonconductive or at least highly resistive. For example, the layer may be a drop, plug, fitting, painted coating or any other disposition of material or materials coupling the wire and the joint.
In another embodiment, the electrical isolation from electrolysis is due to an insulative or highly resistive layer coating all exposed surfaces of the implant member.
In the illustrated embodiment, the implant member comprises a helically wound coil of metal, namely an alloy of platinum. However, the implant may have any physical structure or composition compatible with implantation in the human body.
The invention can alternatively be defined as an apparatus for occluding a body cavity in the presence of an ionic fluid comprising a wire whose distal end is adapted to be positioned in or near the body cavity. The distal end of the wire is fully insulated except for a selected portion serving as an electrolytic joint. Thus, the joint may be a separate structure coupled to the wire, may be a modified portion of the wire itself, or may be an integral part of the wire without modification. A detachable implant is coupled to the distal end of the wire, distal from the joint. The implant is adapted to be positioned in the body cavity. The implant is electrically isolated from electrolysis in the ionic fluid. Substantially only the joint is electrolyzed when current is applied to the wire.
Still further the invention can be defined as an apparatus for occluding a body cavity in the presence of an ionic fluid comprising a wire with a distal end which is insulated. An electrolytic joint is coupled to the distal end. The electrolytic joint is insulated at least in part. A detachable implant is coupled to the electrolytic joint. The implant is not subject to electrolysis in the ionic fluid when current is applied to the wire. The joint is electrolyzed when current is applied to the wire to separate the implant from the wire. The wire and implant may or may not be contiguous with each other, or there may be interlying structures therebetween coupling them together, such as the joint or other structures in the case where the joint is not part of the wire.
The invention is also defined as a method for introduction of an implant into a space within the human body comprising the steps of placing a delivery catheter distal tip near the space within the human body, and introducing an implant assembly. The assembly comprises the implant member and an electrolytically severable joint attached to the implant member""s proximal end. The implant member is electrically isolated from electrolysis. The method includes the steps of placing the implant member into the space, and electrolytically detaching the implant member from the implant assembly.
The invention now having been briefly summarized, turn to the following drawings where like elements are referenced by like numerals.